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<pre class="textdiagram" id="fig27">
     (Next envelope will go here)

          +---------------+
Frame 1   | Reply address |   <----- Envelope (ROUTER)
          +---------------+
Frame 2   | Reply address |   <----- Envelope (ROUTER)
          +---------------+
Frame 3   | Reply address |   <----- Envelope (ROUTER)
          +---+-----------+
Frame 4   |   |   <------ Empty message frame (REQ)
          +---+-------------------------------------+
Frame 5   | Data                                    |
          +-----------------------------------------+
</pre>
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